From: bounce-dv-l-5963@dvcentral.org[mailto:bounce-dv-l-5963@dvcentral.org]On BehalfOf Danny GrizzleSent: Friday, December 20, 2002 2:03 PMTo: DV-LSubject: [dv-l] AUDIO FUNDAMENTALS (was:Speakers for use with FCP)On 12/19/02 12:04 PM, "Don Mitchell"[runtime@wzrd.com> wrote: Can you run through the difference between> monitoring speakers such as the ones youmention> and, say, good quality stereo speakers?The idea behind good audio monitoring isloudspeakers and listeningconditions which reveal the recorded signal in aprecise way. You arelooking for reproduction accuracy so you can"see" what you've got. This isno different than avoiding an inferior displaywhen evaluating video...nobody here would consider using a handheld Casio LCD TV to evaluate3-chip DV footage, would they?Good quality stereo speakers might be useful. 20years ago, there was moreclarity in audio, consumer vs. HiFi. Today,thanks to CDs, consumer audio isvastly improved, while HiFi has all butdisappeared. I would characterizemass-market audio as more or less uniformlymediocre. The public's rush todigital CD audio was about convenience, notquality.I'm not familiar with the speaker you named, anddon't want to get into adebate about the merits of various realloudspeakers, which is entirelysubjective. My only intention is to badmouth lowfidelity computer speakers,completely inappropriate for critical decisionmaking.A quality loudspeaker's job is to reproducesound accurately and with nocoloration. The measurement of success isfrequency response. (Human hearingis from 20 cycles to 20,000 cycles per second.)The difference between goodspeakers and bad speakers is how "flat" theresponse curve is -- lessvariation is good, because it shows the speakeris not adding to or takingaway from the sound signal.HUMAN HEARINGThere are several important things to know abouthow your ears work.All things being equal, when comparing twospeaker systems, most people willbelieve that louder of the two sounds better. Infact, the louder speakermay deliver far less performance. Bottom line:when evaluating speakers, itis important to compare at the same volumelevel, even if this requiresseparate amplifiers and settings.All speakers should be evaluated "flat", with notone controls and noloudness setting engaged.In recent years, electronics designers have beenresearching and exploitingthe "psychoacoustics" of human hearing. Thisgoes beyond straightperformance measurements and gets intoperception. This research is closelyrelated to video compression, both involvingissues of how to eliminate datawithout detection. In the case of audio, thetechnology of psychoacousticsis used to either add or subtract. For instance,MP3 files - compressedaudio for the Internet - are based on lossy datacompression, making filessmaller with little perceived loss in quality.Principles of psychoacousticscan also be used to add sound perception, suchas a video producer who wantsto mix audio so that a cheap 2-inch TV speakeris perceived to make low bassnotes that the laws of physics will not allowsuch a device to make, inreality. Thus, psychoacoutics are useful going &coming for people who knowwhat they are doing, but they have no place in acritical listeningenvironment. Avoid trick consumer-type stereoswith built-in tricks.Tone controls. Most people never exposed to HiFiaudio are surprised tolearn that, at the high end, audiophileequipment provides less controls,not more. The theory goes like this: anybodycommitted to good audio willown superb speakers that do not color the sound.Tone controls -- bass andtreble -- are there only to compensate forinadequate performance of aninferior loudspeaker or a poor listening room.Good sound systems do nothave tone controls or equalizers because theseindicate a deficiency inanother part of the system that should becorrected.Masking Effect. Means this: when more than onesound is present, the humanear will tend to hear the loudest. You can hearsomething whispered intoyour ear normally, but not standing next to ajet engine.SOUND PRODUCTION VS. REPRODUCTIONIn the sound world, production & reproductionare two completely differentanimals. For an audiophile, the objective is torealize the sound created byan artist, reproduced in the listening room asif the artist were present.Thus, no tone controls, etc., because use ofthese would be to introducechanges in the sound, thus not respect theartist's wishes for how theperformance was to be rendered.Sound production, on the other hand, has norules. It is not important if aguitar amplifier loudspeaker is flat or not, solong as it produces a soundthat pleases the artist. Extreme example: JimiHendrix deliberately usedamplifier feedback and distortion, overdrivingelectronics, etc. Cool --these became part of the instrument he wasplaying, and thus the job of theaudiophile's megadollar sound system is toreproduce Hendrix's distortionand feedback perfectly, exactly how he playedit.Fidelity is not a primary consideration forsound reinforcement, and publicaddress (PA) type equipment should never be usedfor critical listening. Infact, speaker designs for sound reinforcementfrequently "creativelydegrade" fidelity for specific purposes. Forinstance, intelligibility ofspoken words is not enhanced by full fidelity.That's why both telephones &AM radio have a particular sound quality, toenhance intelligible speech,and to conserve bandwidth (telephones only).Similar design optimizationsare made in churches and large halls. This maybe hard to discern sincethere are so many ignorant amateurimplementations, but top professionalinstallations are tuned, and not necessarily forperfect accuracy, buttowards a specific set of objectives in aparticular venue.BASIC LOUDSPEAKER DESIGNThere are different types of speaker design. Twoprimary approaches areacoustic suspension and bass reflex. Withacoustic suspension, speakerdrivers are enclosed by a sealed box. BassReflex has a ported box, with anopening allowing air to move to & from theinside of the speaker enclosure.Acoustic suspension speakers are easier todesign for accuracy, but requirea lot of amplifier power. Bass reflex are louderwith smaller amplifiers,but much more difficult to design for flatfrequency response.There are many other loudspeaker designs, somemore exotic than others. Noneof which you are too likely to see. Horns aresometimes used for tweeterelements, but become too big at low frequencies.Interestingly, BoseAcoustic Wave, if you ask me, holds a lot incommon with Klipsch folded horndesigns. True horn designs are excellent, butnot commercially feasible topackage and ship since they require a speakersomething like 20 or 30 feetlong. There are a lot of exotic speakertechnologies on the market, too muchto get into here.One design variation that you *are* likely tosee anymore is variouscross-over networks and subwoofers. JBL was thefirst to popularize thisdesign in a pricy HiFi speaker called the L212(if I remember correctly).Basically, an electronic crossover networkstrips low frequencies from thesignal sent to stereo speakers (or a surroundsystem), and routes lowfrequencies to a dedicated sub-woofer. Basssounds are not directional, so 1speaker is plenty, no need for stereo imaging.Mackie is using sub-wooferswith their studio monitors. I like (but can'tafford) Bob Carver's Sunfirecubes, a really innovative design.PHASE CANCELLATIONSound is a vibration in the air, molecules beingjostled about, to and fro,push and pull. The "push" portion of thevibration is a miniscule amount ofcompression, like a microscopic high pressurefront. The "pull" portion ofthe vibration is called rarefaction, like amicroscopic low pressure front.If push and pull were to occur at the same pointin time, they would net outto zero, no different than summing +1 and -1.The major problems withspeaker installation -- listening room andspeaker position -- is due to thefact that reflecting surfaces such as walls makesound waves bounce andrebound. Once sound is arriving at any givenspot via two different routesof different lengths, it is inevitable thatphase cancellation begins tooccur. Factor into this that various soundfrequencies have variouswavelengths, and you will see that phasecancellation is not uniform, withdead silence at particular listening positions,but rather frequencydependent.Nearfield monitoring (below) addresses thisproblem in a direct manner basedon the human ear's masking effect. Problem is,nearfield monitoring ishighly tuned for a specific listening sweetspot,a single human head. Anyoneelse, see acoustic treatments, below.NEARFIELD MONITORINGThe terms "active" and "nearfield" monitors areoften used in the samebreath, but they are not related.Active loudspeakers contain built-in poweramplifiers, and have become verypopular in recent years. They are not superiorto non-amplified loudspeakersin any way, other than perhaps the conveniencefactor of requiring lesswiring and fewer devices to clutter your desktopor equipment rack.Nearfield is a design strategy in how youposition loudspeakers in yourlistening room. It relies on a basic fact ofphysics (hope I get it right):at twice the distance from a sound source,volume will be 1/4th as loud. Bylocating monitors very close to your listeningposition, away from walls &hard surfaces, sound enters directly into yourears. Reflected sound, thereverberation present in all rooms, is vastlydiminished as a factor incoloration of what you hear, because distancefrom reflecting surfaces is amuch greater distance, resulting in much morevolume fall-off, with theconsequence that your ear's masking effect nolonger hears the lower volumereverberant sound.In essence, nearfield monitoring splits thedifference between headphonesfeeding sound direct into your ear, andconventional loudspeaker placementwhere the reverberant qualities of the roomcombined with specific speakerposition introduce excessive coloration(frequency dependant phasecancellation) into the audio.The thinking behind most active monitors such asthe Mackie HR824 andBehringer Truth is that they will be used in anearfield application.Absolute volume levels are not critical, butlocation in relation to yourlistening position is.ACOUSTIC TREATMENTSWe've all seen photos of acoustic foam and othersound treatments inrecording studios and listening rooms. How dothese work?See various Auralex websites for details:www.auralex.com/>Typical problem for video producers: nearfieldworks great for criticallistening, but not as well for playback togroups of people -- like clients,for instance. Either that, or the video producersimply does not have thespace to position speakers away from wallsappropriate for nearfieldmonitoring. Situations like these are whereacoustic treatments can benefita studio.Here's a short, simple, & practical way todetermine basic acoustictreatment of a given room. It will be perfectlyclear to anyone who has everbanked a shoot on a pool table.With your loudspeakers in final position andalso your listening positionsdefined, take a mirror and hold it flat to thewall. Anyplace on the wallthat you can see the speakers in the mirror froma listening position needsto have acoustic treatment applied to thatportion of the wall. This deadensdirect reflective sound from reaching your earsalong two paths, one directone reflected, producing inevitable phasecancellation.In addition to wall treatments, you willprobably also want to treat corners(vertical -- wall-to-wall -- & horizontalwall-to-ceiling). This traps bassfrequencies. Remember, bass is non-directional,so line of sight is not afactor at low frequencies.===========================Read Jay Rose book for details and insight onaudio, not just studio, butproduction issues, too. BTW - Jay Rose had arecent column thoroughlytrashing the idea of using computer monitorssuch as the clear plastic stickspeakers for video production, although headmired them for industrialdesign and general utility. Some people expousethe theory that you shoulddo everything on a "typical end user TV".Besides the fact that there is nosuch animal, I think this is generally a sloppycompromise that tends tomake a fool out of the producer. The ClintEastwood line, "A man has got toknow his limitations" is more important forproducers than it is for thegeneral populations. It is inexcusable foranyone claming to doprofessional-level video work to be cluelessabout audio, yet we see thisconstantly.Sorry so long, and errors. I'm out of time, sono editing or fact checking.Danny Grizzle---You are currently subscribed to dv-l as:runtime@wzrd.comTo unsubscribe send a blank email to%%email.unsub%%-- (cut off when replying) -----Subscribe, unsubscribe, etc.: http://dv-l.orgSponsors: http://dvcentral.org/Sponsors.htmCritical problems:mailto:postmaster@dvcentral.org--------------------

From: Bill PHere we go again. Have you actually tried a 250 in theelectronic 16:9 mode, or are you just repeating whatyou have read or seen from compressed still pics? Ifind a very small dropoff in quality, with the footagestill very acceptable. It's better in 4:3, but the16:9 degradation is so small that most people probablywouldn't notice it.--- Enrico Quaglia>> Remember the DSR250 doesn't support true widescreen> like the DSR500. What> you're getting is cropped 4:3 with an unacceptable> compromise in terms of> vertical resolution loss. Don't use it unless you> really need to....